1. Field of the Invention.
The present invention relates to corrosion inhibited organic acid compositions which are effective in reducing metal corrosion and methods of using the compositions.
2. Description of the Prior Art.
Subterranean hydrocarbon containing formations penetrated by well bores are often treated with aqueous acid compositions to stimulate the production of hydrocarbons therefrom. One such treatment known as "acidizing" involves the introduction of an aqueous acid composition into a subterranean formation under pressure so that the acid composition flows through the pore spaces of the formation. The acid composition reacts with acid soluble materials contained in the formation thereby increasing the size of the pore spaces and the permeability of the formation. Another production stimulation treatment known as "fracture-acidizing" involves the formation of one or more fractures in the formation and the introduction of an aqueous acid composition into the fractures to etch the fracture faces whereby flow channels are formed when the fractures close. The aqueous acid composition also enlarges the pore spaces in the fracture faces and in the formation.
While acidizing and fracture-acidizing well stimulation treatments have been performed successfully over the years, a continuous problem which accompanies the treatments is the corrosion of metal pumps, tubular goods and other equipment used to introduce the aqueous acid compositions into the subterranean formation to be treated. The expense associated with repairing or replacing corrosion damaged tubular goods and equipment can be very high. The corrosion rate of metal equipment and tubular goods is increased by elevated temperatures encountered in deep formations, and the corrosion results in at least the partial neutralization of the aqueous acid compositions before they react with acid-soluble materials in the formations.
Aqueous acid compositions are also utilized in a variety of other industrial applications to contact and react with acid soluble materials. In such applications, metal equipment and metal surfaces are necessarily also contacted with the acid compositions, and the resulting corrosion of such metal equipment and surfaces is highly undesirable.
A variety of metal corrosion inhibited aqueous acid compositions for carrying out acidizing and fracture-acidizing stimulation treatments in wells and for performing other acidizing operations have been developed heretofore. For example, U.S. Pat. No. 4,498,997 issued to Walker on Feb. 12, 1985 discloses an aqueous acid composition containing a corrosion inhibitor comprising an acetylenic alcohol, a quaternary ammonium compound, an aromatic hydrocarbon and an antimony compound corrosion inhibitor intensifier.
U.S. Pat. Nos. 5,366,643 issued to Walker on Nov. 22, 1994 and 5,411,670 issued to Walker on May 2, 1995 both relate to metal corrosion inhibited aqueous acid compositions which utilize a source of antimony ions to increase the corrosion inhibiting effectiveness of the compositions.
U.S. Pat. No. 5,441,929 issued to Walker on Aug. 15, 1995 discloses a method of protecting metal alloys from acid corrosions utilizing an effective amount of a first inhibitor component including at least one reducing compound and a second inhibitor component including a source of molybdate ions.
While the above described metal corrosion inhibiting formulations have been used successfully as a part of aqueous inorganic acid compositions, e.g., aqueous hydrochloric acid compositions, the corrosion inhibitor formulations have generally been ineffective in organic acid solutions. That is, inorganic acid corrosion inhibitor activators (also referred to as intensifiers) such as formic acid, copper chloride, etc., do not function in organic acid compositions. In this regard, it has been found that the components of commonly utilized corrosion inhibitor formulations used in inorganic acid compositions will not function unless they are activated by a chloride concentration in the composition in the amount of about 5% to about 7% by weight. Because organic acid compositions do not contain appreciable concentrations of chloride, the corrosion inhibitor formulations do not function therein. Thus, there is a continuing need for improved metal corrosion inhibited organic acid compositions and methods of using such compositions in well acidizing applications.